Revert of Remove SkThread.h, include SkMutex.h or SkAtomics.h as appropriate.

src/lazy/SkDiscardableMemoryPool.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDiscardableMemory.h"
 #include "SkDiscardableMemoryPool.h"
 #include "SkImageGenerator.h"
 #include "SkLazyPtr.h"
-#include "SkMutex.h"
 #include "SkTInternalLList.h"
+#include "SkThread.h"
 
 // Note:
 // A PoolDiscardableMemory is memory that is counted in a pool.
 // A DiscardableMemoryPool is a pool of PoolDiscardableMemorys.
 
 namespace {
 
 class PoolDiscardableMemory;
 
 /**
@@ skipping 236 matching lines @@
     return SkNEW_ARGS(DiscardableMemoryPool, (size, mutex));
 }
 
 SK_DECLARE_STATIC_LAZY_PTR(SkDiscardableMemoryPool, global, create_global_pool);
 
 SkDiscardableMemoryPool* SkGetGlobalDiscardableMemoryPool() {
     return global.get();
 }
 
 ////////////////////////////////////////////////////////////////////////////////